Once, “climate-change denier” referred to people who say that climate change isn’t happening, isn’t dangerous, or, if it is happening, that it’s not caused by human activity. But no more. Environmentalists are purging their own ranks to get rid of temporizers. The epithet “climate denier” now gets affixed to insufficiently radical climate affirmers.

In a New York Times opinion page last week, nationally renowned environmentalist Bill McKibben accused President Obama of “catastrophic climate-change denial.” This, for a president who has declared there is “no greater threat” than climate change, who has set about harnessing coal plants with punishing regulations, and who has signaled his intention to pledge at the upcoming U.N. Climate Change Conference in Paris to reduce greenhouse-gas emissions a whopping 28 percent by 2025. The president has himself had some choice words for “deniers” in the past; during his commencement address at the University of California, Irvine, last year, he compared skeptics of anthropogenic global warming to those who believed the moon was “made of cheese.”

Why call our environmentalist in chief a “denier”? Because President Obama just okayed Shell’s license to drill for oil in the Chukchi Sea above the Arctic Circle. This goes against McKibben’s favorite slogan: “Leave it in the ground.” McKibben helms a massive student-driven campaign to get colleges, universities, pensions, churches, and foundations to divest from the fossil-fuel industry. “This is not climate denial of the Republican sort, where people simply pretend the science isn’t real,” McKibben wrote of the president’s behavior. “This is climate denial of the status quo sort, where people...deny the meaning of the science, which is that we must keep carbon in the ground.”

President Obama is not the first environmentalist slammed for striking a rational pose. When Jonathan Franzen published a long essay in the New Yorker in April advocating conservation over climate-change-inspired catastrophism (why not save local birds now rather than ignite them with solar-power plants that may or may not shave off a millionth of a degree of warming in the future?), he was ridiculed for his “global-warming nihilism” and “climate neo-denialism,” and for “peddling climate-change deniers’ favorite myths.” Never mind that he acknowledges global warming’s “supremacy” as the main environmental problem of our time, or that he feels “guilty” and “selfish” whenever he uses a plastic bag.

Naomi Klein, McKibben’s colleague, was recently diagnosed by a Huffington Post blogger with her “own form of climate-change denial” because she ascribes all fault to capitalism and not enough to consumerism. Klein’s blame-the-system rhetoric fires up activists but doesn’t extort high enough personal sacrifices from them. Meanwhile California governor Jerry Brown, who scored 92 percent with the California League of Conservation Voters, earned a scathing denunciation from McKibben because he had kept all environmentalist commandments except for one: He allows fracking.

When the University of Edinburgh declined to divest holdings in fossil-fuel companies, a University College London professor called the decision “a form of denial of the seriousness of the problems facing humanity.” Harvard divestment activists made a similar claim in November when they filed a lawsuit against the Harvard Corporation alleging that the college’s fossil-fuel investments made it complicit in “climate-change denial.”

Even failing to exude sufficient fear of climate change sets off alarm bells with the environmental extremists. A few weeks before the U.K. general elections, the Guardiancriticized candidates for not talking enough about climate change. “There appears to be a robust political consensus around the importance of climate change,” the Guardian wrote, but it is a “silent consensus,” which leaves open space for dissent and denial to creep into the minds of the gullible citizenry.

Last week, University of Western Australia cancelled plans to open a research center affiliated with Bjorn Lomborg’s Copenhagen Consensus after a public outcry that Lomborg “downgrades” climate change. Lomborg and his research team have suggested that investing in universal primary education, halving malaria infections, reducing malnutrition, and cutting indoor air pollution do more good than taking Kyoto-style pledges to reduce greenhouse gas emissions or to hold to 2 degrees of warming. Lomborg thinks that global warming is real and potentially dangerous, but his cost-benefit analysis ruffles ideologues. More than 6,000 Aussies signed a petition pleading “in the name of science” for the university to turn away Lomborg’s “anti-climate science” center.

“Denier” is a slur aimed at discrediting an opponent without having to engage his points. Virtually none of the traditional “deniers” actually think that the climate has never changed or that it hasn’t been warming gradually over the past few decades. The real debate is whether the warming is dangerous. But activists want to avoid that debate. The “denier” label cuts off the oxygen supply of reasoned exchange of ideas among scientists and students. What counts as “denial” is blurry for the greens -- the litany of infractions shifts often -- which allows the movement’s most radical wing to turn the label against their less extreme allies.

Such zeal shows the dogmatism of an increasingly radical environmental movement. This closed-mindedness is the real denial.

This article originally appeared in National Review Online on May 18, 2015.